The ink cartridges of conventional ink jet printers are all provided with a negative pressure mechanism which can generate negative pressure inside the ink cartridge. However, negative pressure is generated from the beginning when the ink cartridge is used for printing and is constantly maintained until the ink is used up. As a result, when the ink cartridge is under the state of negative pressure for a long time, the ink of a printing head can be easily sucked out to damage the printing head and further affect printing quality.
Another kind of ink jet printer adopts the design of non-shaft-type ink supply. A replaceable ink cartridge of such an ink jet printer is positioned below a printing head. The ink is pumped by a suction pump into an irreplaceable ink cartridge above the printing head, which is connected with a nozzle, and the ink is maintained by a negative pressure mechanism. The replaceable ink cartridge of such an ink jet printer only plays a role of accommodating the ink. However, this replaceable ink cartridge is a constant pressure structure, the quantity of ink is detected by a buoy inside the replaceable ink cartridge, and the buoy, due to its own weight, is incapable to detect the quantity of ink accurately when the quantity of ink is small. Therefore, the following function is configured in the program of the printer: when a sheltering part on the other side of the buoy can no longer be detected, the printer prompts the depletion of the ink after printing another 2-3 ML of ink according to an internal counting device.
Based on this function of the printer, a replaceable ink cartridge with an ink bag (as shown in FIG. 1) has been invented for use with such printer. Such an ink cartridge has no air-conducting passage so as not to contact with the air. However, since the demand of detecting the depletion of the ink of the printer needs to be met, the ink bag of the ink cartridge is divided into two parts with one being used cooperatively for detection and the other one being used for accommodating the ink, and the two parts communicate with each other. In order to meet the demand of installation detection of the ink cartridge, the ink bag for detection is sealed by a silica gel film. Due to the different sealing materials of the two parts of the ink bag, which are seldom completely identical to each other in density, toughness and the like, the reflection for suction force is difficult to control, thereby often resulting in that the ink bag for accommodating the ink firstly shrivels and the ink bag for detection then shrivels. In this case, the quantity of ink inside the ink cartridge is less than 2 ml when the detection component detects the depletion of the ink. As a result, the problems about insufficient supply of ink at printing port and burnout of the printing head are generated.